The technical breakthrough of Bednorz and Muller (Z. Phys. B, 64, 189 (1986) ) was the first major improvement in superconducting transition temperature (T.sub.c) in the last decade. This material was a compound of nominal composition La.sub.2-x M.sub.x CuO.sub.y where M=Ca, Sr, or Ba, typically between 0 and 0.3 and y varies with preparation conditions. Subsequently it was reported by Chu et al. (Phys. Rev. Letters, 58, 405 (1987) ) that the material of the composition Y.sub.l.2 Ba.sub.0.8 CuO.sub.y showed the onset of superconductivity in the mid-n degree Kelvin range. Engler et al. (Jn. Am. Chem. Soc., Vol. 109, No. 9, 1987, p. 2848) reported superconducting materials having the composition Y.sub.l Ba.sub.2 Cu.sub.3 O.sub.y where y is sufficient to satisfy the valence requirements of the metals. Engler et al. showed that a variety of superconducting materials could be prepared with the general composition AM.sub.2 Cu.sub.3 O.sub.y, where A was yttrium and/or one or more elements of the lanthanum group (that is, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu) and M was one or more elements of the group Ca, Sr, and Ba. Furthermore, the superconducting properties of these materials are very sensitive to their processing conditions.
Preparation of superconducting composites useful above liquid nitrogen temperature (77.degree. K.) from superconducting ceramics and metals appears unknown prior to the present invention. There is prior art showing, for example, the application of conductor patterns on substrates using metal powder and various metal oxides. See, for example, U.S. Pat. No. 4,001,146. U.S. Pat. No. 4,183,746 shows mixtures of ceramic materials and metals; these compositions are useful in glass making. IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 8, No. 10, March 1986, page 1462, shows an electro paste having increased adhesion. The electro paste includes metal particles, oxides and an organic vehicle. United Kingdom patent application GB No. 2,072,707 shows an electro conductive paste for metallizing, conductive paste for metallizing, containing metal, metal oxides, a binding agent and a solvent. The mentioned references are merely typical of a very large amount of such prior art dealing with metals and ceramics or metal oxides. None of this art, however, deals with superconductors in any way.
Kamioka et al, Japanese Kokai Patent Publication No. 56-85814, July 1981, teaches a process for making an electrode for a condenser. In the process lead barium bismuthate powder is used. The Japanese Patent Publication describes the lead barium bismuthate as "an excellent electrical conductor," and not as a superconductor. U.S. Pat. No. 3,932,315 of Sleight shows a similar composition which is a superconductor at 12.5.degree. K. The Kamioka Patent does not sufficiently describe his process conditions to say that his product was superconducting, but in any event, even assuming arguendo that his product was ever superconducting and that his subsequent processing did not completely destroy the superconductivity, his final product would be totally devoid of superconductivity above 77.degree. K.